Substation telephone circuits



Jan. 31, 1928.

T. G. MARTIN SUBSTATI ON TELEPHONE CIRCUITS Fi edmami 2. 1921 Inuen[Jr-- T517551 EH5: 1n gfl/(wz. gigm nd Jan. 31, 1928.

UNITED STATES PATENT OFFICE.

Tensor e. MARTIN, or onrceeo, rumors, iissrei ion, BY MES NE ASSGNMENTS, TO

AUTOMATEC nLEc'rnrc me, or onroeoc, rumors, A CORPORATION or DELA- WARE.

Application filed March 2, 1921.

l principal object of the invention is to pro vide a circuit arrangementfor a desk tele phone which permits the use of an automatic culling:device with the standard Boll talking circuit, while requiring a minimumnumber of conductors in the cord connectthe telephone proper with thebell box.

It well known tl at good practice re quires some cial provision to bemade for preventing ference between the talking CllClli', and the switchcontrol, or i1npulse transmitting circuit, controlled by the call? ueicc. For instance, it hes always been considered necessary to providemeans for preventing clicks or objectionable noises in the receiver dueto interruptions in the line circuit when the calling device isoperated, and it also desirable to shunt the transmitter while theculling de ice is being operated because its variable resistance is aptto produce an inferior quality of 1moulses. Considerable thought hasbeen expended by inventors in accomplishing these results. In the patentto Willis, #1513; '70, granted August 19, 1919, reissued lvlarch 22,1921, No. 15,070, there is shown adcsh telephone circuit of the typereferred to herein in which a calling device is provided with a singlepair of shunt springs which are effective to bridge the calling deviceimpulse springs directly across the line when the calling device isoperated, thus removing the transmitter from the line, or impulsingcircuit, and shunting the local receiver circuit so that the receiverwill re main quiet. Since these shunt springs connect the calling;device across the line, however, auextra conductor in the cord isrequired to connect with the line side of the primary induction coil.winding, the induction coil being located in the hell box where the lineterminates. Now, it has been found by experiment that the primaryinduction coil winding may well be left in the impulse transmittingcircuit in series with the calling device impulse springs, as its effectis innppreciuble; and it is possible,

therefore, to eliminate one of the cord conductors provided thatsuitable circuit arements are provided tor separately SUBSTATIODTTELEPHQNE CIRGll'ITS.

Serial No. 449,004.

shuntingthe transmitter and receiver within the telephone instrumentitself.

More specifically, then, the present invention may be considered to bean improvement on the circuit shown in the VVillis patent, differingtherefrom-essentially in that the primary winding of the induction coilis included in the impulse transmitting circuit, and in that anadditional contact is provided in the shunt spring assembly, with shuntcircuits adapted to separately shunt the transmitter and receiverwhenever the calling device is operated.

The improved substation circuits will now be described with reference tothe accompanying drawings, in which Fig. 1 is a wiring diagram of anautomatic desl: tele phone and bell box, while Fig. 2 is asimpliiiedcircuit diagram.

Referring first to Fig. 2, the talking circuit as before stated is ofthe well known Bell common battery type. l/Vith the receiver removedfrom the hool'cthe transmitter T and the winding t, of the inductioncoil are bridged across the two line wires 2 and while the receiver Risin series with the winding. 5 of the induction coil and the condenser Cis connected in shunt o f the transmitter. The transmitter and receivercircuits are both normally open and are closed in the usual mannerby theswitchhook H when the receiver is taken ofi? the hook.- Contact springs(fiend 71 are included in the receiver circuit, while contact springs Sand 9 are included in the transmitter circuit.

For receiving incoming signals the ringer M is provided, which isnormally bridged across the line-independent of control by theswitch-hoolc It will be observedthat the ringer bridge includes acondensenand that this condenser is the same one whichis associated withthe receiver R, this con denser being common to the ringer bridge and tothe loesl receiver circuit. I I

Associated with the lower side of theli-ne is a 'subscribers impulsesender, or calling device, which is indicated by thereterencecharacterS. This sender nay be, of th e yp which is wlli l lfil bgd 1.P7 21 5 34 and 35 of Automatic Te'leplionyby Smith and Campbell,published by theMc- Grcwllill Book Company It comprises essentially apair of impulse springs and ill 16 which are controlled by a cam (notshown) through the medium of a linger hold dial (also not shown), andthree shunt springs l2, l3, and ll, together with suitable means forretaining these springs in the position shown in the drawing when thecalling device is not in use, and l'or placing all three springs inengagement with each other when the calling device dial is turned fromits normal position. The ininlsesprings 15 and 16 are connected inseries with the lower line wire 2 and their function is to producemomentary interruptions of the line circuit for the purpose of operatingthe central oi'lice switches. The Function of the shunt springs l2, l3and ll to short circuit or shunt the transmitter T and the receiver itwhile the calling device is being operated to transmit impulses. 'loacconuplish this one spring is connected to the junction ot the receiverand transmitter, while the other two springs are connected to theopposite sides of the transn'iitter and receiver, respectively, and itwill be evident that with the springs connected in this manner when theyare brought into engagement the transmitter and receiver will both beshort circuited, as stated.

In Fig. 1 the circuits have been drawn out in detail, similar partsbeing; indicated by the same reference numerals. For convenience inavoiding crosses in the conductors, some oi the contact springs havebeen rearranged, particularly the calling device springs and theswitch-hook springs, but the circuit is precisely the same and it isbelieved that the change in the positioning ot the springs will cause noconfusion. The apparatus at the right of the drawing, comprising thetransmitter T, the receiver R, the switch-hook H, and the calling deviceS, constitutes the desk telephone proper; while the apparatus at theleft ol the drawing, and comprising the ringer M, the condenser C, andthe induction coil 1, is separate from the telephone and in accordancewith the usual' practice is mounted in the socalled bell box. Thetelephone is provided with the terminal strip P in the base thereof, andthe bcllbor: is provided with the terminal strip P. The various circuitsare completed by means ot a cord which connects the two tern'iinalstrips, which it will be observed conlprises only four conductors. Theline extending to the exchange is connected to the terminal strip P inthe manner clearly shown in the drawinns.

The operation of the substation circuits is as follows: hen the receiveris removed to initiate a call the switchhook contact springs 7 and 9come into engagement, respectively, with the contacts 6 and 8, wherebythe transmitter T is bridged across the line in series with the primarywinding of the induction coil, and the receiver R connected in shunt ofthe transmitter in series with the secondary winding of the inductioncoil and the condenser. Responsive to the closure of the transmitterbridge, current is su iplicd to the transmitter l'l'om a bridged batteryat the central oliice (not shown) over the followingpath: line conductort3. windinn .lof the induction coil l. transmitter T, contact springs 8and U and impulse springs 15 and 16 to the line conductor 2. lhe bridgeat the central ollice, which includes the battery, may also inaccordance with the usual practice include the controlling relay of anautomatic switch, the circuit: oi said relay including, therefore, thetransmitter bridge at the tehmhonc. .lt iollows that the callingsubscriber by suitably nuinipulatinn his calling device dial may producea series ol' interruptions in the circuit oi? the controlling relay tobring about the operation (it W the switch.

it should be noted in this connection that as soon as the dial turned:t'rom its normal position the substation loop is completed over a pathwhich may be traced 'lrou'i the line conductor 3 by way of winding l ofthe induction coil, shunt springs 1:2, 13 and Lt, switch-hook contactsprings 8 and 9, and the impulse springs 15 and 16 to the line conductor2. riable resistance of the transmitter is er;- cluded from the switchcontrol, or impulse transmitting circuit, during the entire time thatthe calling device is in OpQltllllOll and is included again in thebridge across the line only when the calling device dial returns to itsnormal position. At the same time that the transn'littcr is shortcircuited the receiver R is also short circuilcd by means ot the shuntsprings 12 and 1?. The purpose of this'lor one thing is to preventthecurrents induced in the secondary winding from producing clicks ornoises in the receiver. ..'\.lthough this may be considered to be theprimary purpose of short circuitine; the rtu-eiver during impulses, orat least the most obvious one, there is another ad 'antage securedv inthat the high llllPGtltlIlCO receiver wilulinn is excluded trom thelocal circuit of the second ary winding. The secmulary winding of theinduction coil is thus practically short circuited and the impedance ofthe primary winding is thus greatly reduced.

Stu-(warding operations ol' the calling device will new result in theoperation of iudividual automatic switches: at the exchange until. thectmnection is linally completed to the line of the called subscriber. itbeing; understood that all ot' the switches are provided withcontrolling relay bridges which, with the exception oi the bridge in thelast switch. are successively cut oil from the line after theirassociated switches are operated.

The connection having been completed, tuiversttion may he h ild asdesired, ti

It will thus be seen that the vait til) l ll

lil l Cfi talking circuits :tunctioningthe same as usual in such cases.WVhen the receiver is replaced at the end of the conversation,thetransmitter and receiver circuits are broken at the switch-hoot:contacts and further flow ot' direct current through the substation:lrom the exchang is prevented. As a. resuit all the switches at thecentral oliice are released and restored to normal in the usual manner.The substation is now in condition to receive incoming signallingcurrents which may come in over the line conductors 2 and 3 and passthrough the ringer M and the condenser C, whereby the ringer is actuatedto advise the subscriber that he is being called.

it will be seen from the foregoing that I ha vc devised an especial'ladvantageous circuit for an automatic desk telephone which posse=ses allthe desirable features of former circuits and which makes it possible touse a cord con'iprising only fouryconductors for connecting thetelephone itself with the hell be);

l-Iaving described my invention, what I consider to be new and desire tohave protected by Letters Patent will be pointed out in the appendedclaims.

What 1 claim as my invention is:

1. In a substation telephone set, a line circuit, an induction coil, atransmitter and one winding of said induction coil in a bridge of saidline,contact springs ior'clos ing the said bridge, a shunt circuitforsa'id transmitter including a condenser, a second winding 01 saidinduction coil, and a receiver, a second set of contact springs in'theshunt circuit between the receiver and the said second coil winding, asubscribers impulse sender for transmitting current impulses over theline circuit, shunt springs and means for actuating them when theimpulse sender is operated, a shunt circuit controlled by said shuntsprings for directly short circuiting the said transmitter, and anothershunt circuit controlled by said shunt springs for directlyshort-circuiting said receiver;

In a substation telephone set, a line circuit. an induction coil, atransmitter and one winding of said induction coil in a normally openbridge of the line, a local circuit con uecting opposite terminals ofsaid transmitter and including a condenser, a second winding of saidinduction coil, and a receiver, said local circuit being normally open,

said receiver and transmitter normally connected together, means forclosing said bridge and local circuit, a subscribers impulse sender fortransmitting current impulses over the line circuit, shunt springs andmeans "for actuating them when the impulse sender is operated, and shuntcircuits controlled by said shunt springs for short circuiting thetransmitterancl receiver,

said shuntcircuits including threeconductors, one extending to thenormally connected 'ternnnalsot the transimtter and receiver, and theother two extending to the other terminals of the transmitter and receiver, respectively.

3. lna substation telephone set, an induction 'coil, .a transmitter anda circuit there for including one winding of said induction @011, arece1ver and a circuit therefor includ- "ing a condenser, a secondwinding or said induction coil, and the said transmitter, a normallyopen connection in the conductor coin- 111031 to said circuits, a secondnormaily open connection between the receiver and said bridgeol"said'line, a condenser,a windingof said induction coil, and a'recelver in a second bridge oi said line, conductor, common to saidbridges andincluding a second winding of said induction coil, a normallyopen connection in each bridge outside of the common conductor, meansfor closing said connections, a subscribers impulse sender, shuntsprings and means for actuating them when the impulse sender isoperated, and shunt circuits controlled by said shunt springs for shortcircuiting the said transmitter and receiver by connecting the fourterminals thereof directly together.

5. In a substation telephone set, a line circuit, an induction coil, atransmitter in bridge of said line, a condenser, a winding of saidinduction coil, and a receiver in a second bridge of said line, aconductor common to said bridges and including a second winding of saidinduction coil, a normally open connection in each bridge outside of thecommon conductor, means for closing said conncctions, a subscribersimpulse sender, three shunt springs in said sender so connected thatupon the operation of said sender both the transmitter and receiver areshort circuited whether the receiver is oil the hook or not, a terminalstrip providing for the line connections and all connections of saidcondenser and induction coil, a second terminal strip providing for allconnections of the remaining apparatus, and a four conductor cordjoining said terminal strips over which all necessary circuits arecompleted as set ort 6. In a substation telephone set, a line Cir aninduction coil, a transmitter and the primary winding of said inductitmcoil in a bridge of the line, a receiver, a local circuit for saidreceiver including said transmitter, a condenser, andthe secondaryWinding of said induction coil, one terminal of said receirer beingpermanently connected to the junction of the transmitter and the primarywinding of the induction coil, contact springs for closing thetransmitter bridge, other contact springs for closing the receivercircuit. an impulse sender including a pair of impulse springs in serieswith one line conductor, shunt springs in said sender actuated when thesame is in operation, and a shunt circuit controlled by saidshuntsprings for directly short circuiting said transmitter whereby thetransmitter but not the said primary Winding is excluded from the saidbridge during the transmission of impulses.

7. In a substation telephone set, a line circuit, an induction coil, atransmitter and the primary winding of said induction coil in a bridgeof the line, a receiver, a local circuit for said receiver includingsaid transmitter, a condenser, and the secondary Winding of saidinduction coil, one terminal of said receiver being permanentlyconnected to the junction of the transmitter and the pri mary Winding ofthe induction coil, Contact springs for closing the transmitter bridge,other contact springs ior closing the receiver circuit, an impulsesender including a pair of impulse springs in series with one lineconductor, shunt springs in said sender ac tuated when the same is inoperation, a shunt circuit controlled by said shunt springs for directlyshort circuiting said transmitter whereby the transmitter but not thesaid primal winding is excluded from the said bridge during thetransmission of impulses, and a second shunt circuit controlled by saidshunt springs for directly short circuiting: said receiver, whereby thereceiver is pro-- vented from responding to currents induced in thesecondary winding.

8. In a substation telephone set, a line ircult including a callingdevice, a transmitter and one winding of an induction coil in series, alocal circuit irurluding a receiver, a condenser and another winding oi.the induction coil in shunt oi the transmutcr, and shunt springscontrolled by the calling device for permanently closing a shuntcircuit: for the other winding including this condenser While thecalling device being operated.

9. In a substation telephone circuit, a line circuit, a calling device,a transmitter and one Winding of an induction coil in series with theline circuit, a shunt circuit around the transn'iitter and also inseries with the calling device in the line circuit including a receiver,a condenser and amither winding of the induction coil, shunt springscontrolled by the calling device for directly short circuiting thetransmitter and receiver and thereby closing a short circuit around thesecond Winding oi. the indiu-tion coil and the condenser, said shuntcircuits all in series with the calling device in the line circuit.

In witness whereof, I hereunto suiiiscrihe my name this 19th day otFebruary, A. I1.

TALBOT G. MA. tTIN.

Fifi

till

